Fuel block for high temperature electrochemical device

ABSTRACT

A fuel block system which includes a solid fuel. The solid fuel includes one or more of the following: a biomass or a charcoal generated from a biomass; the solid fuel is configured to release a gaseous and electrochemically-active fuel when exposed to heat.

CROSS REFERENCE TO OTHER APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 61/551,086 (Attorney Docket No. PSPIP005+) entitled FUEL BLOCK FORHIGH TEMPERATURE ELECTROCHEMICAL DEVICE filed Oct. 25, 2011 which isincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

Fuel cell systems (such as solid oxide fuel cell systems) use heat,oxygen, and fuel to generate electrical power. Fuel cell systemstypically operate in sterile, controlled environments where purified,gaseous fuels are piped in. The environment is typically sealed so thatgases or materials (e.g., other than the gaseous fuel and oxygen) do notcontaminate the system and/or the flow rate of the gaseous fuel and/oroxygen introduced is carefully controlled (e.g., using valves). New fuelcell systems which are able to be used in a wider range of environmentsand/or conditions are being developed for campers, hunters, and otherswho do not have access to a power grid. These rugged fuel cell systemsare designed to hold solid fuels (e.g., animal dung, biomass,agricultural waste, and/or wood chips). Accessories related to such newfuel cell systems would be desirable, for example which improve oroptimize the power generation of these new fuel cell systems anddecrease performance degradation over time.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a diagram showing an embodiment of a fuel cell systemconfigured to hold a fuel block in a fuel chamber and operate in a hotzone.

FIG. 2 is a diagram showing an embodiment of a solid oxide fuel cellsystem.

FIG. 3 is a diagram showing an embodiment of a fuel block having awrapper.

FIG. 4 is a graph showing an embodiment of power production as afunction of time for a fuel block with and without a polyolefin shrinkwrap wrapper.

FIG. 5 is a graph showing an embodiment of power production as afunction of time for a fuel block with and without a paper wrapper.

FIG. 6 is a graph showing an embodiment of power production forcharcoals made from various types of biomass.

FIG. 7 is a graph showing an embodiment of power production as afunction of time for various performance additives.

FIG. 8 is a graph showing an embodiment of power production forcharcoals pyrolyzed at various temperatures.

FIG. 9 is a diagram showing an embodiment of a fuel block having anintegrated lid.

FIG. 10 is a diagram showing an embodiment of a fuel block having anintegrated lid with an opening.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess; an apparatus; a system; and/or a composition of matter. In thisspecification, these implementations, or any other form that theinvention may take, may be referred to as techniques. In general, theorder of the steps of disclosed processes may be altered within thescope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

A fuel block configured to be inserted into a fuel cell system isdescribed herein. Such fuel blocks include biomass (e.g., plantmaterial, vegetation, wood, forest and wood plant residuals, leaves,grasses, agricultural wastes, energy crops, algae, pits, shells, husks,rinds, agricultural or food processing byproducts, paper processingbyproducts, animal waste, chemicals and/or material separated orextracted from biomass, etc.) and/or charcoal generated from pyrolyzinga biomass. Charcoal is the residue obtained by removing water and othervolatile constituents from biomass and is obtained by pyrolysis.Pyrolysis is a thermochemical decomposition of matter at elevatedtemperatures without the participation of oxygen or with insufficientoxygen for complete combustion of the matter. Although some ingredientsand/or manufacturing processes related to fuel blocks may be similar tothose for charcoal briquettes (e.g., for barbequing), the fuel blocksdescribed herein are different from barbeque charcoals in that fuelblocks are designed to optimize electrical power production and lifetimeof a fuel cell system. This may include, for example, releasing one ormore gaseous, electrochemically-active fuels (e.g., H₂ and CO) duringelevated temperature operation (e.g. greater than 550° C.-650° C.) whichare used in the fuel cell system's electrochemical reaction to generateelectrical power and/or releasing oxygen (also used in theelectrochemical reaction). The fuel blocks described herein pyrolyze andrelease gaseous, electrochemically-active fuels in close proximity to afuel cell system and may release undesirable compounds that degrade fuelcell power output and/or accelerate corrosion of metal components of thefuel cell system (e.g. stainless steel) thus decreasing useful life ofthe system. This degradation of the fuel cell and/or corrosion of metalcomponents is a result of elements other than carbon, hydrogen, andoxygen in the fuel block, for example chlorine, and so the fuel blockprovided has a composition modified for improved gasification duringoperation and/or decreased fuel cell degradation and/or decreased metalcorrosion. In contrast, barbeque charcoals are designed to ignitequickly, burn completely, and/or optimize heat release. Although a fuelcell system's electrochemical reaction requires heat, the fuel blockrecited herein is not intended to be the primary or main heat source forthe electrochemical reaction. As such, different ingredients may be usedand/or an ingredient may serve a different purpose.

FIG. 1 is a diagram showing an embodiment of a fuel cell systemconfigured to hold a fuel block in a fuel chamber and operate in a hotzone. In the example shown, fuel cell system 102 is a solid oxide fuelcell system. Solid oxide fuel cell systems use heat (e.g., from heatsource 106), oxygen (e.g., coming from the top opening of container 104and/or air hole 110), and fuel (e.g., gaseous fuels released by fuelblock 112 or alternatively some solid biomass, such as animal dung,wood, or agricultural byproduct, which is inserted into a fuel chamber)to generate electrical power. Although this example shows heat from afire, barbeque grill, and/or cooking stove, other types of heat sourcesmay be used, including (but not limited to) a heat exchanger, a boiler,a furnace, an engine, a nuclear power facility, a concentrated solardevice, and so on.

Fuel cell system 102 and fuel block 112 are heated by heat source 106.Fuel cell system 102 provides a relatively small amount of power to, forexample, operate an LED lamp, radio, a fan for a cookstove, or charge acell phone battery. In this example, fuel cell system 102 is configuredto sit at or near the bottom of container 104. One example of container104 is a ceramic jiko stove common to East Africa. Other examples ofcontainer 104 include barbeque grills (e.g., Weber grills); highefficiency cookstoves; stone or clay fireplaces; 3-stone fires; or sandor dirt campfires.

In this example, fuel cell system 102 is configured to hold a singlefuel block 112 in a single fuel chamber. In some other embodiments,multiple fuel blocks are able to be inserted into a single fuel chamber.For example, a company may make two models of fuel cell systems butsells fuel blocks in a single size. The larger fuel cell system may havea fuel chamber that can fit two, three, or more fuel blocks whereas thesmaller fuel cell system has a fuel chamber that fits a single fuelblock. In some embodiments, a fuel cell system has two or more fuelchambers. In some embodiments, a fuel block is inserted into eachchamber. In other embodiments, a single fuel block is shaped such thatit fills or partially fills multiple fuel chambers. Fuel cell system 102is able to operate with biomass (e.g., wood and/or animal dung) orcharcoal inserted into a fuel chamber, but electrical power productionmay not be as good as when fuel block 112 is used.

When heat source 106 is ignited, fuel cell system 102 and fuel block 112heat up. Air flows from the bottom or sides of container 104 and passesto the oxygen electrode (not shown) of the fuel cell(s). As fuel block112 in the fuel chamber heats up, gaseous fuel species are released byfuel block 112 to the fuel cell(s), causing fuel cell system 102 toproduce electrical power. The power is transferred out of the hot zoneby power transfer leads 114 (e.g., to a rechargeable battery, a fan, anLED light, or a cell phone charger). If not replenished, the heat fromheat source 106 will typically last from 30 minutes to several hours.Fuel cell system 102 produces power when the temperature is aboveapproximately 550° C. with better power production occurring above650-700° C. As such, the time that fuel cell system 102 is hot enough toproduce power is generally shorter than the time during which heatsource 106 is hot enough for cooking, space heating, etc., and may be asshort as a few minutes. As heat source 106 heats fuel cell system 102above about 550° C., electrical power is generated. As the temperaturecontinues to rise, the power output increases. After some time, thetemperature of heat source 106 and fuel cell system 102 begins todecrease and the power output also decreases. Thus, a typical sessionresults in a “wave” of power generated. In some instances the session isshort and fuel block 112 will not release all of the available fuelspecies and a portion of fuel block 112 will remain. Reusing theremaining portion of a previously used fuel block results in decreasedpower output and potentially causes damage to the fuel cell system.Techniques or features for distinguishing a new fuel block from apartially used fuel block ensures that an unskilled user does not reusea fuel block. In other instances the session is long and most or all ofthe carbon or hydrocarbon content of the fuel block has been released.It is desirable that the remaining material, such as ash, not degradethe fuel cell or damage the fuel cell system.

Although fuel cell system 102 is able to use biomass in the fuelchamber, it is desirable to produce as much electrical power aspossible. Fuel block 112, which includes biomass or charcoal generatedfrom pyrolyzing a biomass, is designed to do this. For example, fuelblock 112 is highly active in the production of gaseouselectrochemically-active fuel species (e.g., H₂ and CO) over a broadtemperature range. This has the desirable result of increasing theinstantaneous power output, as well as increasing the period of time(or, using another metric, increasing the range of temperatures) overwhich electrical power is produced. Since total energy is the integralof (e.g., instantaneous) power over time, total electrical energyproduction is improved (e.g., compared to fuels which may be foundnaturally at a camp site or other location, such as wood, charcoal,and/or animal dung). In some embodiments, fuel block 112 interacts withgaseous products from the fuel cell reactions (such as H₂O and/or CO₂)to generate more gaseous fuels (such as H₂ and/or CO) for instance viareforming.

FIG. 2 is a diagram showing an embodiment of a solid oxide fuel cellsystem. In the example shown, fuel block 206 is inserted into fuelchamber 202 and is exposed to the fuel electrode (not labeled) of fuelcell 200. Lid 204 is optional but in this example is used to containfuel block 206 (e.g., in case the fuel cell system falls over, lid 204keeps fuel block 206 from falling out). Fuel block 206 is sized so thatit is easily inserted into fuel chamber 202. It is not necessary forfuel block 206 to touch or come into contact with cell 200. Althoughfuel chamber 202 is able to be partially or completely filled withpowder, chips, or chunks (e.g., of biomass), a single fuel block iseasier to load and controls and/or optimizes the amount of fuel insertedfor each operation run. This may help ensure a fuel cell system has theproper amount of fuel to ensure better performance.

In contrast to other fuel cell systems employing purified gaseous fuelssuch as hydrogen or methane that are continuously piped in to generateelectrical power, the solid oxide fuel cell system described herein (oneembodiment of which is shown in FIG. 2) utilizes batch loads of solidfuel in a fuel chamber (e.g., fuel chamber 202). Solid fuels may containelements (e.g., other than carbon, hydrogen, and/or oxygen) that canform gaseous, solid, and/or liquid matter that can affect the operationof the fuel cell system. In the example shown, the size and compositionof solid fuel block 206 determines the availability of gaseous fuels forthe fuel cell system as well the amount of other material that mayinteract with the fuel cell and/or metallic components of the fuel cellsystem. The fuel cell system utilizes a batch of fuel block 206 during atypical electric power generation session and if the power generationsession is sufficiently long then fuel block 206 may be completelyutilized and the fuel chamber 202 exposed to partially oxidizing oroxidizing conditions. It has been found that exposure of fuel cell 200and/or metallic components of the fuel cell system to these conditionscan accelerate performance degradation and/or metal corrosion if thefuel block contains deleterious species such as chlorine, or othercorrosion-promoting species.

In some embodiments, compounds containing chlorine are minimized in fuelblock 206, for example by selecting a low chlorine-content biomass or byremoving chlorine compounds from the biomass and/or charcoal by rinsingwith water (or, more generally, some liquid). In some embodiments, achlorine removal process is not intended to remove all chlorine, butinstead reduces (e.g., significantly) the amount of chlorine or chlorinecompounds. It has been found that alkali and alkaline earth chloridesdegrade the performance of a fuel cell system and reducing the chlorinecontent of a fuel block improves the lifetime of a fuel cell system.Common chlorides such as sodium chloride (NaCl), potassium chloride(KCl) and calcium chloride (CaCl₂) have been found to be corrosion anddegrade the performance of a fuel cell system.

In some embodiments, a finely divided biomass and/or charcoal derivedfrom biomass has been compressed to form a fuel block configured to beinserted into a fuel cell system. A fuel block may be formed into aself-supporting object, such as a block, pill, sheet, pellet, or tablet.Compressing a fuel block increases the density and improves the handlingand ease of insertion into the fuel chamber. Alternatively, otherforming operations such as extrusion, tape-casting, tableting, etc. maybe used to form the fuel block. A self-supporting object is easier topackage and ship and the fuel block is preferably classified asnon-hazardous for shipping by land, sea, and/or air.

In some embodiments, a fuel block has a wrapper. The following figuredescribes some example wrappers.

FIG. 3 is a diagram showing an embodiment of a fuel block having awrapper. In some embodiments, wrapper 302 contains solid fuel 300. Insome embodiments, wrapper 302 provides aesthetics. In some embodiments,wrapper 302 makes a fuel block clean or easy to handle (e.g., so thatthe fuel does not rub off on the hands of a user). In some embodiments,wrapper 302 controls the shape of a fuel block so it fits easily into afuel chamber. In some embodiments, wrapper 302 seals a fuel block sothat it does not absorb moisture, or release fuel or additives, eitherof which may decrease the power generated. In some embodiments, wrapper302 establishes a “unit” of fuel so that the fuel chamber of a fuel cellsystem is not under-filled or over-filled. In some embodiments, wrapper302 changes color, texture, or burns off during operation to clearlydistinguish an unused fuel block from a used fuel block. Any of thesefeatures may be provided, even in the absence of a wrapper.

In various embodiments, wrapper 302 is impermeable or porous; clear,translucent or opaque; and/or loosely or tightly wrapped. Some examplewrapper materials include paper, and polymer films such as acrylic,polyolefin, etc. In various embodiments, wrapper 302 is applied bywrapping, painting, spraying, dip-coating, shrink-wrapping or othermeans.

The following figures show some example performance graphs with wrappersmade of various materials.

FIG. 4 is a graph showing an embodiment of power production as afunction of time for a fuel block with and without a polyolefin shrinkwrap wrapper. In some embodiments, a fuel block includes a polyolefinshrink wrap wrapper. In this example, a first fuel block was prepared bymixing charcoal powder with 5% (by weight) acrylic and 13% (by weight)polyethylene glycol-6000MW binders. The powder and binder mixture waspressed at 15 kpsi to form a rigid pellet of fuel. One such pellet wasshrink wrapped with polyolefin film and another identical pellet wasleft unwrapped. Graph 400 shows power production as function of time forthe pellet without a wrapper (solid line) and the pellet with shrinkwrapped with polyolefin (dashed line). The power was recorded during athermal cycle comprising of increasing the temperature at 30° C./min to750° C., holding the temperature constant for 10 minutes, and cooling at5° C./min to room temperature.

FIG. 5 is a graph showing an embodiment of power production as afunction of time for a fuel block with and without a paper wrapper. Insome embodiments, a fuel block includes a paper wrapper (e.g., made ofcoffee filter paper). In this example, a fuel block was created bywrapping 4.5 g of loose charcoal powder in an envelope constructed fromcoffee filter paper; a similar batch of fuel was created without awrapper. The same heating-steady-cooling cycle described above was used.Graph 500 shows power production as function of time for the fuel batchwithout a wrapping (solid line) and the fuel block wrapped in coffeefilter paper (dashed line).

In some embodiments, a fuel block includes one or more binders. Forexample, if the fuel block uses solid fuel in the form of powder, dust,or pieces, a binder may be added to hold the fuel block together (e.g.,for shipping, handling, and use by an end user). In one example, abinder is added to solid fuel in the form of powder. The mixture is thenpressed, cast, extruded, rolled, tamped, and/or dried into the desiredshape. Such processing may also compress the fuel powder, increasing thedensity of the fuel block. As a result, for a given fuel chamber size,more fuel can be inserted as a compressed fuel block, compared to loosepowder. This results in higher power generation by the fuel cell duringoperation.

Some example binders include polymer binders (e.g., acrylic,polyethylene glycol, polyvinyl alcohol, hydroxypropylcellulose,paraffin, microcrystalline cellulose, lignin, sucrose, dextrin, lactose,and glycerin) and inorganic binders (e.g., such as clays,aluminosilicates, carbonate salts, and polyphosphates).

Various types of biomass may be pyrolyzed to obtain charcoal for use ina fuel block. In some embodiments chemicals and/or material separated orextracted from biomass or a specific portion of a biomass (e.g.,heartwood, hemicellulose, lignin, bean, husk, etc.) may be pyrolyzed toobtain charcoal for a fuel block. The following figure shows examplepower performance using various types of biomass pyrolyzed to obtaincharcoal for use in a fuel block. In some embodiments, biomass typeshaving better/best performance (e.g., from the following figure) areused to create charcoal for use in fuel blocks.

FIG. 6 is a graph showing an embodiment of power production forcharcoals made from various types of biomass. In the example shown,various types of biomass were dried in an oven and then pyrolyzed (e.g.,sealed in an airtight, non-flammable container, such as a stainlesssteel container, and flushed with an insert gas, such as argon) at 400°C. for 3 hours. Biomass types experimented with include: mesquiteheartwood, corn kernels, corn cob, corn husk, bamboo, coffee beans,potatoes, mushrooms, tea leaves, banana fruit, and banana peel. Theresulting charcoals were used to fuel a fuel cell held at 0.65V ateither 650° C. or 800° C. for 2 hours. All provided useable fuel for thefuel cell. As shown in graph 600, charcoals derived from coffee beansand potatoes provided the best performance. In some embodiments, a fuelblock (e.g., used to power a fuel cell system) includes charcoal derivedfrom coffee beans. In some applications, using charcoal derived fromcoffee beans is desirable because some forms of the source biomass arereadily available (e.g., used coffee grounds from coffeehouses). In someembodiments, a fuel block includes charcoal derived from potatoes. Insome embodiments, potato leftovers or byproducts are used to generatecharcoal (e.g., potato skin waste from a factory which does not keep theskins). Other kinds of biomass byproducts or waste from (for example)manufacturing processes or refinement processes may be used to generatecharcoal for a fuel block. In some embodiments chemicals and/or materialseparated or extracted from a biomass may be used.

In addition to biomass and/or charcoal generated from a pyrolyzedbiomass, a fuel block may include an additive that improves the releaseof electrochemically-active fuel species from the fuel block. In someembodiments, an additive includes a potassium-containing compound.Potassium containing compounds include but are not limited to potassiumoxide, potassium carbonate, potassium bicarbonate, potassium hydroxide,potassium nitrate, potassium phosphate, and potassium citrate. In someembodiments, a potassium-containing compound does not contain chlorine,for example potassium chloride (KCl) contains chlorine. In one exampleformulation, additives are 0-20 weight percent (wt %) of the fuel block.In some cases, less than 10 wt % is more attractive than 0-20 wt %. Insome cases, 1-5 wt % is more attractive than less than 10 wt %. This maybe because while in general increasing the amount of additive improvesthe release of electrochemically-active fuel species, some experimentshave found that increasing the amount of potassium-containing compoundadditive beyond 10 wt % can increase degradation of the fuel cellsystem.

The following figure shows that in at least some embodiments, includinga potassium-containing compound in a fuel block improves the performanceof a fuel cell system. Some other additive examples include an alkali,an alkaline element, a hydrocarbon, a calcium-containing compound, alithium-containing compound, an iron-containing compound, or acobalt-containing compound.

FIG. 7 is a graph showing an embodiment of power production as afunction of time for various performance additives. Some charcoalsderived from biomass demonstrate a dramatic decline in the release ofgaseous fuel species at temperatures below 800° C. (e.g., without thepresence of performance additives). It would be desirable to maximizethe release rate of gaseous fuel from a fuel block over the entiretemperature range for which the fuel cell is hot enough to function(e.g., 550° C. and higher). In some embodiments, a fuel block includesone or more performance additives which function by catalyticallypromoting the conversion of solid fuel to gaseous fuel species, or bythemselves releasing gaseous fuel species.

A fuel cell system was loaded with approximately 15 g of fuel preparedby mixing mesquite charcoal powder with: nothing; 33% (by weight) oil;10% (by weight) potassium compound; or 33% (by weight) oil and 10% (byweight) potassium compound. Various oils were experimented with,including: mineral oil, kerosene, candle wax, Crisco, and natural oilsderived from olive, palm, soybean, and coconut. Variouspotassium-containing compounds were used, including: potassiumcarbonate, potassium bicarbonate, potash (the water soluble portion ofcharcoal ash). The power generated by the fuel cell operating with eachfuel type was recorded during a thermal cycle of heating at 30° C./minto 750° C., holding the temperature for 10 minutes, and then cooling at5° C./min to room temperature. Graph 700 shows the performance of thebest performing mixtures from the experiment compared to pure charcoal.Charcoal alone (i.e., with no performance additive) is shown with anunbroken line; charcoal and mineral oil is shown with a dotted line;charcoal and potassium carbonate is shown with a dashed line; charcoal,mineral oil, and potassium carbonate is shown with a bold, dashed line.

The additives shown in graph 700 improve the peak power achieved duringthe hold at 750° C., as well as the power produced during heating andcooling. The total time of useful power production was increased witheach of the additives. The addition of mineral oil and potassiumcarbonate provided the largest performance improvement.

In some embodiments, a potassium-containing compound (or other additive)is mixed together with a charcoal made from biomass. It was alsodetermined during this experiment that potassium-containing compoundsare most effective when they are mixed with the charcoal powder. Simplyplacing a potassium-containing compound inside the fuel chamber beforeor after loading the charcoal powder (i.e., without mixing the charcoaland potassium-containing compound together) did not result in asignificant power improvement.

In some embodiments, a potassium-containing compound in a fuel blockacts as a binder (e.g., to maintain the shape of a fuel block duringshipping and handling).

A biomass may be pyrolyzed at a variety of temperatures when creatingcharcoal. The following figure shows some performance values forcharcoal pyrolyzed at various temperatures. In some embodiments,charcoal is pyrolyzed at the temperature(s) having better or bestperformance as shown below.

FIG. 8 is a graph showing an embodiment of power production forcharcoals pyrolyzed at various temperatures. In the example shown,mesquite heartwood was pyrolyzed at various temperatures. The wood wassealed in a relatively airtight, stainless steel container, which wasflushed with flowing argon (more generally, an inert gas). Other typesof inert gas may be used, such as nitrogen. The container was heated ina furnace at 5° C./min to various temperatures ranging from 300° C. to600° C. The temperature was held for 3 hours and then the container wascooled to room temperature. The resulting charcoal was ground into apowder, and used to fuel a solid oxide fuel cell system. The temperatureof the fuel cell system was held at 800° C. and 0.65V for two hours. Theamount of charge produced was recorded and is shown in graph 800. In theexample shown in graph 800, the highest charge was produced from woodpyrolyzed in the range of 400-500° C. In some embodiments, charcoalincluded in a fuel block is generated by pyrolyzing biomass at atemperature in the range of 400-500° C.

In some embodiments, a moist inert gas is used during pyrolyzation. Inone experiment, mesquite heartwood was pyrolyzed according to theprocedure described above at 400° C. for 3 hours. Two batches wereproduced: one with dry argon flowing during pyrolysis, and one withmoist argon flowing during pyrolysis. The argon was moistened bybubbling argon gas through a water bath at room temperature, resultingin a mixture of approximately 97% Ar and 3% water. The resultingcharcoals were used to fuel a fuel cell system held at 0.65V at either650° C. or 800° C. for 2 hours. At 650° C., the charcoal pyrolyzed inmoist argon produced 1.9 times more charge than that pyrolyzed in dryargon. No significant difference was observed at 800° C. It is believedthat the addition of water creates hydrogenated charcoal species duringpyrolysis, and these species release hydrogen-rich gaseous fuel speciesduring operation. It is further believed that these species arecompletely released at temperatures below 800° C., so they did notcontribute to power generation at 800° C.

FIG. 9 is a diagram showing an embodiment of a fuel block having anintegrated lid. In the example shown, fuel block 400 includes lid 402.Benefits of a lid may include: containing electrochemically-active fuelspecies; preventing or reducing transport of oxygen to the fuel; or,preventing external contaminants (such as the heat source fuel) fromentering the fuel chamber. In embodiments where a fuel block includes awrapper, a lid may be attached to the fuel block and then enclosed in awrapper, or alternatively attached to a wrapper after wrapping. Someexample materials for a lid include (but are not limited to): clay,ceramic, metal, and glass. In some embodiments, multiple fuel blocks areattached to a single lid (e.g., for fuel cell systems with multiple fuelchambers where the fuel blocks attached to the lid are aligned with thefuel chambers).

In some embodiments, a lid which is included with a fuel block is stickyor tacky where it comes into contact with fuel chamber 904 (e.g., thelid has a layer of adhesive, such as wax and the lip of the fuel chamberis pressed into the wax, connecting the lid and the fuel chamber).Alternatively, a portion of the fuel block (with or without a lid) issticky or tacky. In some applications, this is attractive because itpermits a lid to be used no matter the shape of a fuel chamber. Overtime, fuel chambers may warp (e.g., because of the extreme heat from afire) or bend (e.g., from being dropped or stepped on). A lid which isused over and over may become misaligned with the fuel chamber over timeand it may be difficult to close or seal the reused lid. In otherapplications, the is attractive because it permits fuel blocks to beloaded into the bottom or side of the fuel chamber and prevent them fromfalling out during subsequent placement of the fuel cell system near theheat source.

Another advantage of having an integrated lid is that it may be easierto remove a spent fuel block and insert a new fuel block when a fuelcell system is still hot and/or in a hot zone. For example, a camper mayhave an abundant supply of firewood and is able to keep a campfire lit.The camper may wish to remove a spent fuel block while the fuel cellsystem remains in the campfire. Using tongs, the camper grabs on to thelid and pulls out the spent fuel block and inserts a new fuel block(e.g., again using tongs and grabbing the lid). In contrast, a reusablelid which must be buckled, clipped, or screwed on to a fuel chamberwould require fine motor skills which would be difficult to performwhile the fuel cell system is still hot and/or in a hot zone.

FIG. 10 is a diagram showing an embodiment of a fuel block having anintegrated lid with an opening. In the example shown, lid 1000 includesopening 1004. The solid fuel (e.g., charcoal from biomass,potassium-containing compound, and any other ingredients in the fuelblock) extends through opening 1004. After exposure to a heat source(e.g., coals in a cookstove), the solid fuel shrinks, exposing opening1004. This permits a user to look through opening 1004, see how muchsolid fuel remains, and decide when (if desired) to remove the fuelblock and replace it with a new fuel block.

In some embodiments, a fuel block has some sensory indication (e.g., avisual or tactile indication) which enables a user to monitor theconsumption of the solid fuel and/or decide when to replace a fuel block(e.g., when looking through opening 1004). In some embodiments, a fuelblock includes a volatile binder, where the binding of fuel block isrelatively weak and falls apart after use. In some embodiments, certaintypes of biomass or charcoals are included where such biomass orcharcoals produce enough ash during use to effect a visible colorchange.

In some embodiments, a fuel block includes one or more indicatoringredients which changes color after use to clearly distinguish anunused fuel block from a used fuel block. Some example indicatoringredients include transition metal oxides, metallic flakes, dyes, andcolored polymers. The indicator can be a change in color, surface finish(shiny to rough), reflective particles (sparkles), etc. In one example,fuel blocks were prepared by pressing charcoal powder and a binder. Thefuel blocks were then painted with a mixture of acrylic emulsion andred/orange iron oxide (Fe₃O₄). The fuel blocks were then used in a fuelchamber placed in a ceramic jiko stove for one cooking session. Aftercooling, the fuel blocks were removed from the fuel chamber. The ironoxide had turned dark black from reduction (e.g., to FeO or Fe₂O₃). Insome embodiments, an indicator ingredient may be contained only in thewrapper, dispersed throughout the solid fuel itself, etc.

Fuel block 1006 additionally includes mesh 1002. Mesh 1002 keeps theremnants of the solid fuel together so that if a fuel block is removedfrom a fuel chamber, all of the remnants of the solid fuel are removedfrom the fuel chamber. This enables a new fuel block to be insertedwithout being blocked by remnants from previously used fuel blocks. Insome embodiments, mesh 1002 is made of metal wire.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A fuel block system, comprising: a solid fuelwhich includes one or more of the following: a biomass or a charcoalgenerated from a biomass, wherein the solid fuel is configured torelease a gaseous and electrochemically-active fuel when exposed toheat.
 2. The fuel block system of claim 1, wherein at least one of thefollowing is naturally low in chlorine: the biomass or the charcoalgenerated from a biomass.
 3. The fuel block system of claim 1, wherein achlorine removal process is performed on at least one of the following:the biomass or the charcoal generated from a biomass.
 4. The fuel blocksystem of claim 3, wherein the chlorine removal process includes washingwith a liquid to remove chlorine.
 5. The fuel block system of claim 1further comprising a wrapper.
 6. The fuel block system of claim 1,wherein at least one of the following is finely divided: the biomass orthe charcoal generated from a biomass.
 7. The fuel block system of claim6, wherein the fuel block system is formed into a self-supportingobject.
 8. The fuel block system of claim 7, wherein the fuel blocksystem is formed into one or more of the following: a pellet, a block, apill, a sheet, or a tablet.
 9. The fuel block system of claim 1 furthercomprising a potassium-containing compound, wherein thepotassium-containing compound is 0-20 weight percent of the fuel blocksystem.
 10. The fuel block system of claim 9, wherein thepotassium-containing compound includes one or more of the following:potassium carbonate, potassium bicarbonate, potassium hydroxide,potassium nitrate, or potassium sulfate.
 11. The fuel block system ofclaim 1 further comprising an oil.
 12. The fuel block system of claim 1further comprising an oil and a potassium-containing compound, whereinat least two of the following are mixed together: the solid fuel, theoil, or the potassium-containing compound.
 13. The fuel block system ofclaim 1 further comprising an indicator ingredient configured to changecolor during one or more of the following: exposure to heat or releaseof the gaseous and electrochemically-active fuel.
 14. The fuel blocksystem of claim 1 further comprising a lid.
 15. The fuel block system ofclaim 1, wherein the charcoal generated from a biomass is generatedusing pyrolysis in the one or more of the following ranges of 300-600°C. or 400-500° C.